The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.
In a variety of downhole applications, flow isolation valves are used to isolate formations for reasons related to prevention of fluid loss, underbalanced well control, lubricator valve applications, and other reasons that benefit from the ability to isolate regions along a wellbore. The flow isolation valve may be a ball valve designed to provide a bidirectional pressure seal. The ball valve is moved from an open flow position to a closed position by passing a shifting tool through its center. Typically, a shifting tool is attached below perforating guns on a gun string such that when the perforating guns are pulled out of hole, the shifting tool shifts the ball of the formation isolation valve to a closed position. Once closed, the well head pressure may be safely bled off while the subject formation remains isolated. This allows the well to be suspended for days or even months.
However, the ball of the formation isolation valve also creates a barrier onto which debris is often deposited. The debris can clog the mechanism and ultimately prevent the shifting tool from dislodging the debris during efforts to open the ball. Additionally, existing ball designs employ parts that are difficult to manufacture due to dimensional instability and tight tolerance requirements. The tight tolerances and the complex designs are employed to achieve both rotation and translation of the ball within the ball valve structure. Because of the difficult design requirements, many of the parts manufactured for construction of the ball valves are scrapped, and that leads to additional expense and inefficiency.